Many digital cameras have autofocus capability. Autofocus may be fully automatic such that the camera identifies objects in the scene and focuses on the objects. In some cases, the camera may determine which objects are more important than other objects and subsequently focus on the more important objects. Alternatively, autofocus may utilize user input specifying which portion or portions of the scene are of interest. Based thereupon, the autofocus function identifies objects within the portion(s) of the scene, specified by the user, and focuses the camera on such objects.
To achieve market adoption, the autofocus function must be reliable and fast such that every time a user captures an image, the camera quickly brings the desired portion, or portions, of the scene into focus. Preferably, the autofocus function is sufficiently fast that the user does not notice any delay between pressing the trigger button and image capture. The autofocus is particularly important for cameras having no means for manual focus, such as compact digital cameras and camera phones.
To this end, camera manufacturers are developing image sensors with on-chip phase detection, i.e., image sensors with integrated phase detection capability via the inclusion of phase-detection auto-focus (PDAF) pixels in the image sensor's pixel array.